392 Prof. T. Sternj Hunt — On Cambrian and Silurian. 



some places resting upon the nearly vertical Longmjaid rocks, and 

 in others upon the Llandeilo-flags, the Caradoo proper or Bala group, 

 and the Lower Llandovery beds. Again, in South Wales, near 

 Builth, the May Hill sandstone or Upper Llandovery rests upon 

 Lower Llandeilo beds ; while at Noeth Grrug the overlying formation 

 is traced transgressively from the Lower Llandovery across the 

 Caradoc to the Llandeilo. These important results were soon confirmed 

 by Kamsay and by Sedgwick. (Ibid. vol. iv. p. 236.) The May Hill 

 sandstone often includes, near its base, conglomerate beds made up 

 of the ruins of the older formation. To the north-east, in the typical 

 Silurian country, it is of great thickness and continuity, but gradually 

 thins out to the south-west. 



There exists, moreover, another region where not less curious 

 discoveries were made. About forty miles to the eastward of the 

 typical region in South Wales appear some important areas of 

 Silurian rocks. These are the Woolhope beds, appearing through 

 the Old Eed Sandstone, and the deposits of Abberley, the Malverns 

 and May Hill, rising along its eastern border, and covered along 

 their eastern base by the newer Mesozoic sandstone. The rocks of 

 these localities were by Murchison in his Silurian System described 

 as offering the complete sequence. When however it was found that 

 his Caradoc included two unconformable series, examination showed 

 that there was no representative of the older Caradoc or Bala group 

 in these eastern regions, but that the so-called Caradoc was nothing 

 but the Upper Llandovery or May Hill sandstone. The immediately 

 underlying strata, which Murchison had regarded as Llandeilo, or 

 rather as the beds of passage from Llandeilo to Cambrian, and had 

 compared with the north-west pai'ts of the Caermarthenshire sections 

 (Sil. Sys. p. 416), have since been found to be much more ancient 

 deposits, of Middle Cambrian age, which rest upon the crystalline 

 hypozoic rocks of the Malverns, and are unconformably overlaid by 

 the May Hill sandstone. We shall again revert to this region, 

 which has been carefully studied and described by Prof. John 

 Phillips. (Mem. Geol. Surv., vol. ii. part 1.) 



What then was the value and the significance of the Silurian sec- 

 tions of Murchison, when examined in the light of the results of the 

 Government surveyors ? The Llandeilo rocks, having throughout 

 the characteristic OrtJiis so much insisted upon by Murchison, were 

 shown to be the base of a great conformable series, and to the east- 

 ward, in Shropshire, to rest on the upturned edges of the Longmynd 

 rocks ; while westward, near Bala, they overlie unconformably the 

 Lingula-flags, and in the island of Anglesea repose directly upon the 

 ancient crystalline schists. According to the author of the Silurian 

 System, there existed beneath the base of the Llandeilo formation a 

 great conformable series of slaty rocks, into which this formation 

 passed, and from which it could not be distinguished either zoologi- 

 cally, stratigraphically, or lithologically. The sequence, determined 

 from what were considered typical sections in the valley of the 

 Towey in Caermarthenshire, as given by Murchison, for several 

 years both before and after the publication of his work, was as 

 follows : 1. Cambrian ; 2. Llandeilo-flags ; 3. Caradoc sandstone ; 



